Check if a user Is fan of a Facebook page

Question

After logged in I am trying to return if the user is either not a fan of a Facebook page, but the result is always "undefined". But if I replace "return" to "alert" works perfectly.

function pageFan()
{
    FB.api({ method: 'pages.isFan', page_id: '175625039138809' }, function(response) {
        showAlert(response);
    });
}

function showAlert(response)
{
    if (response == true) {  
        return 'like the Application.';
    } else {
        return "doesn't like the Application.";
    }
}

var like = pageFan();
document.getElementById('debug').innerHTML = like; //return undefined

score 1 · Answer 1 · edited May 23 '17 at 12:21

This question has already been answered.

Relevant Javascript:

$(document).ready(function(){
      FB.login(function(response) {
      if (response.session) {

          var user_id = response.session.uid;
          var page_id = "40796308305"; //coca cola
          var fql_query = "SELECT uid FROM page_fan WHERE page_id = "+page_id+"and uid="+user_id;
          var the_query = FB.Data.query(fql_query);

          the_query.wait(function(rows) {

              if (rows.length == 1 && rows[0].uid == user_id) {
                  $("#container_like").show();

                  //here you could also do some ajax and get the content for a "liker" instead of simply showing a hidden div in the page.

              } else {
                  $("#container_notlike").show();
                  //and here you could get the content for a non liker in ajax...
              }
          });


      } else {
        // user is not logged in
      }
    });

response.session is outdated, instead the correct way is: response.authResponse — Philip, Apr 26 '12 at 18:43

Etienne Perot · Answer 2 · 2012-04-26T18:14:50.407

0

That's because the return in showAlert is not returning "into" the pageFan function. The showAlert function is passed as a callback, meaning it will be called later, outside of pageFan's execution. I think you need to read more about callback functions and asynchronous programming.

function showAlert(response)
{
    if (response == true) {  
        document.getElementById('debug').innerHTML = 'like the Application.';
    } else {
        document.getElementById('debug').innerHTML = "doesn't like the Application.";
    }
}

edited Apr 26 '12 at 18:14

answered Apr 26 '12 at 17:27

Etienne Perot

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Ok, I understand, but what is the solution? – Eron Venter Apr 26 '12 at 17:41
The solution is to modify the `debug` element within `showAlert`. Edited answer – Etienne Perot Apr 26 '12 at 18:15

Check if a user Is fan of a Facebook page

2 Answers2